In recent years, there is a demand for faster data transfer speed on a wide area network (WAN) to respond to the business globalization, the aggregation of data centers to servers, and the spread of the cloud utilization and the mobile terminal.
Before describing a technique for achieving faster data transfer speed, an example of packet exchanges executed between a client and a server when reading a file is described. FIG. 16 is a diagram for illustrating Related Technique 1. A processing procedure of Related Technique 1 is based on the common internet file system (CIFS). As illustrated in FIG. 16, a client 10, when reading a file of a server 20, transmits request packets 10a to 10d and receives response packets 20a to 20d. The request packets 10a to 10d and the response packets 20a to 20d include, for example, various commands, parameters, and statuses.
For example, when reading a file A, the client 10 sequentially executes processing of transmitting the request packet 10a and then receiving the response packet 20a, and processing of transmitting the request packet 10b and then receiving the response packet 20b. Also, the client 10 executes processing of transmitting the request packet 10c and then receiving the response packet 20c. 
When ending the reading of the file A, the client 10 executes processing of transmitting the request packet 10d and then receiving the response packet 20d. 
As described with reference to FIG. 16, Related Technique 1 has a problem that a useless latency occurs due to the exchange of the request packet and response packet. For example, a round-trip time (RTT) taken until the client 10 ends the processing of reading the file A is expressed by Formula (1). In Formula (1), a RTT1 represents a time from when the client 10 transmits the request packet 10a until when the client 10 receives the response packet 20a. A RTT2 represents a time from when the client 10 transmits the request packet 10b until when the client 10 receives the response packet 20b. A RTT3 represents a time from when the client 10 transmits the request packet 10c until when the client 10 receives the response packet 20c. A RTT4 represents a time from when the client 10 transmits the request packet 10d until when the client 10 receives the response packet 20d. RTT=RTT1+RTT2+RTT3+RTT4  (1)
Next, Related Technique 2 for achieving faster data transfer is described. FIG. 17 is a diagram for illustrating Related Technique 2. As illustrated in FIG. 17, Related Technique 2 provides a dummy client 35 and a dummy server 45 between a client 30 and a server 40.
The dummy client 35 analyzes the CIFS protocol in advance and generates a sequence table 50. The sequence table 50 is a table configured to associate the request packet and a subsequent predicted packet with each other. The request packet is a request packet transmitted from the client 30. The subsequent predicted packet is a request packet predicted to be transmitted from the client 30 next to the request packet transmitted from the client 30.
For example, in the example indicated by the sequence table 50 of FIG. 17, a request packet including a command “open” and a parameter “1234” is associated with a subsequent predicted packet including a command “getinfo” and a parameter “004”. Thus, when the request packet including the command “open” and the parameter “1234” is transmitted from the client 30, it may be predicted from the sequence table 50 that the request packet including the command “getinfo” and the parameter “004” is to be transmitted next.
Upon receiving a request packet from the client 30, the dummy client 35 compares the request packet to the sequence table 50 to identify the subsequent predicted packet. Upon identifying the subsequent predicted packet, the dummy client 35 transmits the subsequent predicted packet to the server 40 before receiving a next request packet from the client 30.
For example, in the example illustrated in FIG. 17, upon acquiring a request packet 30a from the client 30, the dummy client 35 transmits the request packet 30a and predicted packets 35a, 35b to the server 40. The predicted packet 35a is a request packet which is predicted from the request packet 30a, and the predicted packet 35b is a request packet which is predicted from the predicted packet 35a. 
The request packet 30a and predicted packets 35a, 35b reach the server 40 via the dummy server 45. The server 40 transmits a response packet 40a corresponding to the request packet 30a, a response packet 40b corresponding to the predicted packet 35a, and a response packet 40c corresponding to the predicted packet 35b to the client 30.
The response packets 40a to 40c reach the dummy client 35 via the dummy server 45. The dummy client 35 transmits the response packet 40a corresponding to the received request packet 30a to the client 30. Thereafter, the dummy client 35, when receiving the request packet 30b from the client 30, transmits the response packet 40b to the client 30. The dummy client 35, when receiving the request packet 30c from the client 30, transmits the response packet 40c to the client 30.
As described with reference to FIG. 17, before receiving request packets 30b, 30c from the client 30, the dummy client 35 transmits predicted packets 35a, 35b to the server 40 in advance and receives the response packets 40b, 40c in advance. Execution of such processing allows the client 30 to receive response packets relative to the request packets 30b, 30c faster than Related Technique 1, and thereby reduction of the RTT is achieved.
For example, related techniques are disclosed in Japanese Laid-open Patent Publication Nos. 2011-039899 and 2013-218505.